Preheat oven to 335°F (170°C). Grease a 9×5-inch loaf pan and line it with a parchment sling for easy removal.
Spread the nuts on a small baking sheet and toast in the heating oven for 6–8 minutes until fragrant. Cool, then chop if not already chopped; reserve 2 tablespoons for topping.
In a large bowl, mash the bananas with the brown sugar until mostly smooth with a few small bits for texture.
Whisk in the eggs one at a time, then the vanilla. Slowly whisk in the cooled melted butter in a thin stream until the mixture looks glossy and well combined.
In a separate bowl, whisk the flour, baking soda, salt, and cinnamon. Add the orange zest and rub it into the dry mixture with your fingertips to release its oils.
Add the dry mixture to the banana mixture and fold gently with a spatula just until a few small streaks of flour remain. Fold in the chopped nuts, saving the reserved 2 tablespoons for the top.
Let the batter rest for 10 minutes to hydrate the flour. Scrape into the prepared pan, smooth the top, sprinkle with the reserved nuts, and score a shallow line down the center with a buttered knife to encourage an even split as it rises.
Bake for 58–68 minutes, rotating the pan after 40 minutes, until the loaf is deep golden and a tester inserted near the center comes out with a few moist crumbs (not wet batter).
Cool in the pan for 15 minutes, then lift out using the parchment and cool completely on a rack for at least 45 minutes before slicing.